Chitin, poly (β(1-4)-N-acetyl-D-glucosamine) is a natural polysaccharide of mayor importance. This biopolymer is synthesized by an enormous number of living organisms including crustaceans, insects, fungi, filamentous fungi and yeasts. Considering the amount of chitin produced annually in the word, it is the most abundant polymer after cellulose.
The main commercial sources of chitin have been crab and shrimp shell. In industrial processing, chitin is extracted from crustaceans by acid treatment to dissolve calcium carbonate followed by alkaline extraction to solubilize proteins. The most important derivate of chitin is chitosan, obtained by (partial) deacetylation of chitin in the solid state under alkaline conditions (concentrate NaOH) or by enzymatic hydrolysis in the presence of chitin deacetylase. Under controlled conditions, chitin and chitosan can be polymerized to yield water soluble derivatives such as chitin-oligosaccharides (ChOS) and chitosan-oligosaccharides (COS), respectively.
These oligomers are recognized for their bioactivity; including anti-tumor, bactericidal and fungicidal activity, eliciting chitinase and regulating plant growth. Chitin is involved in host defense against bacterial invasion, has been used to prepare affinity chromatography column and is widely used to immobilize enzymes and whole cells.
On account of its biodegradability, non-toxicity, physiological inertness, antibacterial properties, hydrophilicity, gel-forming properties and affinity for proteins, chitin has found applications in many areas other than food such as in biosensors. Chitin—based materials are also used for the treatment of industrial pollutants. Chitin can be processed in form of film and fiber. Regenerated chitin derivative fibers are used as binders in the paper making process, fiber improves the breaking strength of paper. However, the main development of chitin film and fiber is in medical and pharmaceutical applications as wound-dressing material.
When the degree of deacetylation of chitin reaches about 50% it become soluble in aqueous acidic media and is called chitosan. Chitosan is the only pseudo-natural cationic polymer and thus, it is used many applications. Being soluble in aqueous solution, it is largely used in different applications as solutions, gels, or films and fibers. The main investigations of chitosan concern its preparation with varied molecular weights and deacetylation, the dependence of its solution properties on the deacetylation, the preparation of derivatives and applications.
Chitosan is much easy to process than chitin, but the stability of chitosan materials is generally lower, owing to their more hydrophilic character and, especially, pH sensitivity. Chitosan and its derivatives have various functional properties that have made it possible for them to be used in many fields including, food, cosmetic, biomedicine, agriculture, environment protection and wastewater management. The most important fields where the specificity of chitosan must be recognized are cosmetic, pharmaceutical and biomedical applications. Drug delivery applications include oral, nasal, parenteral and transdermal administration, implants and gene delivery.
Another point to note is biological activity in regard to agriculture since chitosan exhibits antivirus and antiphage activities. It inhibits the growth of bacterial and bacterial infection, and stimuli the natural defenses in plant. Also is used for the seed coating, frost protection, time releases of fertilizers and nutrients into the soil.
Even though the chitosan is known to have important functional activities, the high molecular weight and high viscosity may restrict the uses in some special fields, particularly in medicine and the food industry, because most animal intestines, especially human gastrointestinal tract, do not possess enzymes such as chitinase and chitosanase, which directly degrade the β-glucosidic linkage in chitin and chitosan. Unlike chitosan, its hydrolyzed products and chitosan oligosaccharides (COS) are readily soluble in water duo their shorter chain length and free amino group in D-glucosamine units. The low viscosity and great solubility of COS at neutral pH have attracted the interest of many researchers to utilize chitosan in its oligosaccharide form. Especially, in food and nutrition areas have emphasized their ability to improve food and quality and human health progression.
Chemical and enzymatic methods are widely used for COS production and among them chemical hydrolysis is used more commonly in the industrial-scale production. However, chemical hydrolysis has some drawbacks to be commercialized, due to development of toxic compounds, higher risk associated with the environment pollution, and lower production yield. The enzymatic processes are generally carried out in bath and are preferable over chemical methods. This is due to minimized adverse chemical modifications of product during enzymatic hydrolysis.
Other product generated from chitin is glucosamine, IT can be used in agriculture, has shown that the presence of glucosamine in the composition of the soil cause an increment of trichomes absorbent, which is manifested in increased the vigor of the plant. The first reaction can be observed is a strengthening of the tips that take a deep green color, with the border of slightly curly leaves. This is because, when applying glucosamine in the soil, the plant induce a response similar to that which would result when la plant try to defender itself of the attack from fungus, nematodes or insect without these really exist.
In the area of medicine, glucosamine has been used for the treatment for arthritis, promotes the development of the cartilaginous tissue, is used in the reconstruction of cartilage. Glucosamine is involved in the formation of nails, tendons, skin, eyes, bones, ligaments and heart valves, is also implicated in the production of collagen and proteoglycans.